Three jurors from the Jodi Arias trial said the sentencing phase was "absolutely awful" after they were unable to agree on whether the woman they had found guilty of first-degree murder should get the death penalty or life in prison.

"We can't come to a decision, and it was gut-wrenching. It was absolutely awful," said Diane Schwartz, a retired 911 operator, who for the duration of the five month trial was known as Juror No. 6.

The jury took a short time to convict Arias of first-degree murder in the 2008 shooting and stabbing death of her ex-boyfriend, Travis Alexander, but when it came to the sentencing phase, they were split.

Schwartz, along with fellow jurors Kevin Spellman and Marilou Allen-Coogan, spoke exclusively with ABC News about the grave responsibility that they said ended with a deadlock of eight jurors voting in favor of the death penalty and four supporting life in prison for Arias.

All three said they favored giving Arias the death penalty, however, determining a sentence of life or death for the 32-year-old was their most difficult decision.

"It was a very trying experience," said Spellman, a banker who was known as Juror No. 13. "How do you weigh a person's life?"

"For me, it was the brutality and then the way that he was treated after death and shoved in a shower and left," Allen-Coogan added. "That's pretty brutal."

Arias, 32, had been branded a liar by the prosecution because she initially denied killing Alexander, then claimed two years later that she killed him in self-defense, citing Alexander's physical and emotional abuse.

Some of the most intense moments during the trial came over the 18 days when Arias took the stand and described her relationship with Alexander.

"Based on what we saw and the evidence presented, it was very apparent that we weren't being told the truth in a lot of the matters, and there was a lot of cover-up," Allen-Coogan said, adding that she believed Arias was playing to the jury.

"The state proved their case. It was premeditated," she said.

Schwartz agreed, "What she was telling me just didn't weigh true to me."

"I noticed pretty early on, when Jodi tells a story, she babbles," said Spellman. "She has no poker face."

After three days of deliberations, the jury's hung verdict was read Thursday, leaving the case open and the jury dismissed.

"I felt like we had failed the system," Schwartz said. "As I walked out, I remember looking towards the prosecution table. I thought, 'They won't even look at us.'

"I immediately, as I was stepping down, told them, 'I'm sorry,'" she said. "It was heartfelt because I was. I was very sorry."

Despite the deadlock, Spellman said he believes no matter what sentence Arias receives, she is dying.

"She is sentenced to death no matter what," he said.

Arias' fate is now left up to the prosecutor, who will decide whether to retry the penalty phase. If he decides to try again for the death penalty, a new jury will be selected and both the prosecution and defense will present evidence and arguments over what sentence Arias should receive.

The retrial, in which Arias could either be sentenced to death or to life in prison, with or without the possibility of parole, would begin July 18.

If the prosecution chooses not to retry the penalty phase, Arias will get life in prison, either with or without parole.